In the electronic arts, particularly, for example, in coherent or Doppler radar systems, there is a need for multi-frequency signals, that is, a "comb of frequencies," which are co-existent in time and locked to a single reference frequency. Such a comb of frequencies includes integer multiples of the reference frequency, that is, 1, 2, 3, 4,..., etc., multiples of the reference frequency.
In the past, step recovery diodes have been used in such multi-frequency signal generators. However, such step recovery diodes cause very substantial phase jitter, that is, frequency modulated (FM) noise, on the frequency comb components. Such jitter is considered highly undesirable.